1. Field of the Invention
The present invention relates to an aqueous dispersion recording medium, and more particularly to a writable optical data recording medium having at least a light-absorbing layer and a light-reflecting layer on a light-transmitting substrate.
2. Description of Related Art
Conventional writable optical data recording media are essentially structures in which a light-absorbing layer consisting of an organic dye or the like is located on a light-transmitting substrate having spirally formed pregrooves, and a light-reflecting layer consisting of a metal film or the like is located on the light-absorbing layer, as described in Japanese Patent Publication 7-105065, for example.
Data is recorded when laser-based recording light is directed onto the optical data recording medium from the substrate side so as to allow the energy to be absorbed by the light-absorbing layer, and recording pits are formed as a result of the heating and decomposition of the dye in the light-absorbing layer, thermal deformation of the substrate, and so forth.
Such writable optical data recording media are generally known as "CD-Rs." Such CD-Rs characteristically are capable of only a single recording, which cannot be erased, and are highly compatible with read-only CDs (compact discs) and CD-ROMs, making them quite popular, particularly in the data processing fields.
The growth of data as well as the increasing sophistication and complexity of data processing have led to more rapid recording on optical data recording media and more rapid read-out in the last several years. 6.times. recording devices and 15.times. read-out CD-ROM drives became commercially available by the end of 1996 in the CD-R market.
Efforts have been made to obtain an optical data recording medium in which the recording speed is 6 times faster, assuming, for example, 6.times. high speed recording, where the medium is irradiated with high output laser light in time increments that are about 1/6 the time corresponding to the pit length nT of the EFM signal, resulting in the recording of signals within a stipulated range of pit lengths 3T to 11T.
Accordingly, precision greater than that of conventional equal-speed recording is needed in order to control the T recording pit length of recording devices.
Since it is also necessary to form pits of a prescribed length in a fraction of the conventional time on recording media, the effects of heat and thermal interference during recording are far greater than in the past.
Thermal irregularities produced during such high speed recording thus result in worse jitter, causing deviation in pit length.
In Japanese Laid-Open Patent Application 4-192131, for example, dyes such as benzoindodicarbocyanin and indodicarbocyanin are mixed as the light-absorbing substance in the light-absorbing layer.
That is, the benzoindodicarbocyanin is added as a light-absorbing agent, and the indodicarbocyanin is added as an agent to increase the reflectivity. The benzoindodicarbocyanin absorbs the recording light and thus decomposes, but the indocarbocyanin does not absorb the recording light and is thus not decomposed. Sufficient modulation thus cannot be achieved or the jitter deteriorates when the light-absorbing layer has a film thickness of less than 100 nm. In other words, these problems come about when there is a lower proportion of molecules absorbing laser light in the film.
These problems occur when two or more dyes are mixed as the light-absorbing substance and also when just one dye is used, and are the effects of molecular and association absorption in the absorbance spectra described below.